If when you open Nord Vpn, the update message will come out, please install new update otherwise when you try to connect to any servers Nord Vpn will not work and will not connect.

Look screenshots here below to understand:

You can quit Nord Vpn from notifications bar icon -> "Quit app", but don't have logout from "settings" inside program, otherwise if some satanic scumbag have changed password, it will not work anymore. And so doing this way every time you open the program will still work.